forum administration

There is an issue with forum administration. If you just login as Admin and try to create a new topic or reply to a post and click the submit button it logouts the admin mentioning that you are not logged in. Its happening only with chrome browser on some machine. I am unable to figure out the reason. I am using Fluxbb 1.4.2.Please help.

Thanks,Sushil Pandey

History

during my debug i found that somewhere the value $pun_user['is_guest'] is true i.e. the cookies expires and the last login of user on the viewtopic.php is shown 1970. I am unable which code is responsible to expire the cookies.